1. Field of the Invention
The present invention relates to a method of manufacturing a pipe body by performing a bending operation on a metal plate, to a pipe body manufactured by the method, and to an image forming apparatus using the pipe body.
2. Discussion of the Background
A method of manufacturing a pipe body having a rectangular cross section has been proposed in a Published Japanese patent application 2001-286934. In the Published Japanese patent application 2001-286934, as illustrated in FIGS. 1A and 1B, an intermediate product 41 is formed by bending a metal plate 40 having a pair of edges 40a and 40b parallel to each other. As illustrated in FIG. 1B, the intermediate product 41 includes three walls 42, 43a, and 43b which construct the pipe body's walls except an upper wall. The upper wall is formed by joining the edges 40a and 40b to each other. Specifically, the wall 42 constructs a bottom wall of the pipe body, and the walls 43a and 43b construct side walls of the pipe body and adjoin the wall 42 (hereafter referred to as adjoining walls 43a and 43b). In the intermediate product 41, each angle θ1 formed between the wall 42 and the adjoining wall 43a or 43b is made obtuse, so that the edges 40a and 40b are away from each other.
Next, as illustrated in FIGS. 1C and 1D, external forces are applied to the adjoining walls 43a and 43b, and thereby the wall 42 is curved outward and the edges 40a and 40b are brought into intimate contact with each other. Then, referring to FIG. 1E, another external force is applied to the curved portion of the wall 42 while applying pressure to a surface 45 of the upper wall including a junction 44 of the edges 40a and 40b, and thereby the wall 42 is deformed to be flat. As a result, a pipe body 46 is obtained as a completed product.
In the above-described manufacturing method of a pipe body, a spring back force that maintains the edges 40a and 40b of the intermediate product 41 in close contacted condition remains at a surface 47 of the wall 42, allowing the edges 40a and 40b to closely contact each other without welding.
As described above, to flatten the wall 42 and to enhance the planarity of the surface 45 of the upper wall and the surface 47 of the wall 42, an external force is applied to the wall 42 while applying pressure to the surface 45. When applying an external force to the wall 42 while applying pressure to the surface 45, deformation such as buckling may occur on a surface 49 of the adjoining wall 43a and a surface 50 of the adjoining wall 43b in the pipe body 46. Such deformation may be caused by the following reasons: (1) the strength of the adjoining walls 43a and 43b against the external force is insufficient due to the uneven hardness of the material for the metal plate 40, and (2) the external force is excessively exerted when the bottom dead center position of a mold 48 pressing the surface 45 of the upper wall is lower than an assumed position due to the fluctuation of process conditions. The deformation may affect the quality of a product especially when the surfaces 49 and 50 are needed to be formed with accuracy and when holes are formed in the surfaces 49 and 50 with high accuracy. Accordingly, the quality inspection of products may be required.
However, the above-described deformation does not necessary occur constantly even in the same production lot. Therefore, when manufacturing products with high accuracy, the inspection of all completed products needs to be performed, thereby increasing the manufacturing cost of a pipe body.
Therefore, it is desirable to provide a manufacturing method of a pipe body in which the surfaces of the pipe body do not deform when external forces are applied thereto at the time of press process, thereby at least reducing inspection of a completed pipe body, and suppressing increase in manufacturing cost for a pipe body even with high accuracy.